Constant Envelope Property Research Articles

Energy Consumption Analysis for Continuous Phase Modulation in Smart-Grid Internet of Things of beyond 5G.

Wireless sensor network (WSN) underpinning the smart-grid Internet of Things (SG-IoT) has been a popular research topic in recent years due to its great potential for enabling a wide range of important applications. However, the energy consumption (EC) characteristic of sensor nodes is a key factor that affects the operational performance (e.g., lifetime of sensors) and the total cost of ownership of WSNs. In this paper, to find the modulation techniques suitable for WSNs, we investigate the EC characteristic of continuous phase modulation (CPM), which is an attractive modulation scheme candidate for WSNs because of its constant envelope property. We first develop an EC model for the sensor nodes of WSNs by considering the circuits and a typical communication protocol that relies on automatic repeat request (ARQ)-based retransmissions to ensure successful data delivery. Then, we use this model to analyze the EC characteristic of CPM under various configurations of modulation parameters. Furthermore, we compare the EC characteristic of CPM with that of other representative modulation schemes, such as offset quadrature phase-shift keying (OQPSK) and quadrature amplitude modulation (QAM), which are commonly used in communication protocols of WSNs. Our analysis and simulation results provide insights into the EC characteristics of multiple modulation schemes in the context of WSNs; thus, they are beneficial for designing energy-efficient SG-IoT in the beyond-5G (B5G) and the 6G era.

Joint time-frequency domain equalization of MSK signal over underwater acoustic channel

Minimum shift keying (MSK) shows better bandwidth efficiency than the phase shift keying owing to its high bandwidth usage efficiency and constant envelope property. The performance of frequency-domain block linear equalization (FD-BLE), which is commonly used for MSK communication, is limited in complex time-varying underwater acoustic (UWA) channel. In this paper, a time-domain adaptive decision feedback equalization (TD-ADFE) is proposed to address issues pertaining to MSK communications over UWA channel. Further joint time–frequency domain equalization (JTFDE) built on TD-ADFE and BLE is proposed to further reduce the bit error rate (BER). The proposed method can effectively track the time-varying UWA channel through the updated equalizer coefficient according to the output of de-mapper. Numerical simulation shows that the JTFDE performed better than TD-ADFE and FD-BLE over time-varying UWA channel by approximately 2 dB when the BER was 1 × 10−3.The sea trial results verified the proposed JTFDE and demonstrated that the BER of JTFDE was 82.5% and 88.9% lower than that of TD-ADFE and FD-BLE, respectively.

Interference Gaussianization: Time-Domain Inter-Symbol Spreading for Blind Adaptive Array Signal Source Identification

This paper proposes a novel blind adaptive array (BAA) interference suppression scheme incorporated with a time-domain symbol spreading (TISS). It can expand an operational region of BAA irrespective of input signal-to-interference power ratio (SIR) conditions. Independent component analysis (ICA) and constant modulus algorithm (CMA) are expected as the promising BAA approaches to suppress unknown interference which is extensively caused due to the small cell densification and spectrum superposing between a plurality of wireless communication systems. These BAA algorithms basically require an input SIR to be larger than 0 dB to suppress interference by capturing the desired signal appropriately. The proposed scheme applies TISS to the transmission signal for the desired user and then de-spreads it at the receiver side. It Gaussianizes statistical inherence of the interference signals and can bring beneficial effects; reducing the kurtosis for ICA as well as collapsing the constant envelope properties for CMA. Such intentional modification to the interference signals can improve the capture performance of the desired signal and realize its effective identification even at SIR <; 0 dB. Its fundamental effectiveness is presented through various perspectives such as input SIR, symbol amount, and modulation orders.

Coplanar Turbo‐FSK: A Flexible and Power Efficient Modulation for the Internet‐of‐Things

As the Internet‐of‐Things (IoT) has expanded, multiple solutions have attempted to address the issues of the Low Power Wide Area (LPWA) networks physical layer. In a previous work, we proposed the Turbo‐FSK, a constant envelope modulation with orthogonal alphabet that allows the receiver to operate at very low levels of power (high sensitivity performance) and very low levels of energy per bit Eb. The scheme was demonstrated to approach Shannon’s limit as close as 0.29 dB. However, the scheme lacks flexibility in terms of spectral efficiency (always lower than 10−1 bits/s/Hz), especially compared to the recently standardized Narrow‐Band IoT (NB‐IoT) solution. In this work, we propose an evolution of the initial scheme, so‐called Coplanar Turbo‐FSK (C‐TFSK). In order to increase the spectral efficiency of the system, two new features are introduced: a modulation combining linear and orthogonal properties where only subsets of the alphabet are orthogonal and a puncturing mechanism. Several aspects of the scheme are then studied under asymptotic hypothesis, such as the influence of the linear component of the alphabet and the effects of puncturing. The high flexibility in terms of spectral efficiency, the short distance to Shannon’s limit, and the constant envelope property make the C‐TFSK a serious contender for the physical layer of the IoT.

Symmetric 10 Gb/s wavelength reused bidirectional RSOA based WDM-PON with DPSK modulated downstream and OFDM modulated upstream signals

A 10Gb/s bidirectional wavelength division multiplexing passive optical network (WDM-PON) with reflective semiconductor optical amplifier (RSOA) based colorless optical network unit (ONU) is proposed and analyzed for next generation gigabit class optical access network. Differential phase shift keying (DPSK) modulated signal is used in downstream and further reused as a seeding wavelength for upstream data modulation. By exploiting the constant envelope property of DPSK seed signal, the re-modulation noise in upstream receiver is effectively minimized without employing any constraint on extinction ratio of downstream signal. Orthogonal frequency division multiplexing (OFDM) signal is used in upstream transmission to overcome the limited bandwidth (∼1GHz) response of RSOA remodulation. The results show that the proposed 10Gb/s symmetric WDM-PON can achieve good performance over 25km fiber transmission with error free operation in downstream and bit error rate (BER) lower than forward error correction (FEC) limit in upstream.

Spatial Diversity, Low PAPR and Fast Decoding for OFDM using L2-Orthogonal CPM ST-Codes

Orthogonal Frequency Division Multiplexing (OFDM) schemes provide high data rates and good robustness against frequency selective fading for communication systems. Space-Time Block Coding (STBC) is an efficient way to introduce space-time diversity in Multiple-Input Multiple-Output (MIMO) systems. Using non-linear modulations such as Continuous Phase Modulation (CPM) with its constant envelope property may be a way to construct MIMO OFDM systems that alleviates the typical Peak to Average Power Ratio (PAPR) issue of OFDM. However, CPM based systems are usually plagued by decoding complexity issues. In this paper, we introduce space-time-frequency diversity techniques based on L2-orthogonal multi-h CPM Space-Time codes designed for OFDM transmission. We benchmark these codes under frequency selective Rayleigh channels and show how they achieve full spatial diversity at full rate for any number of antennas, good spectral compactness, low PAPR and robustness to frequency fading. Furthermore, L2-orthogonality allows fast decoding with complexity growing only linearly in the number of Tx antennas.

Non-orthogonal Amplify and Forward Relay Selection Systems with Distributed Space–Time Trellis Coded Continuous Phase Modulation

Most of the works on cooperative systems with or without relay selection have focused on linear modulations such as phase shift keying and quadrature amplitude modulation. Whereas, continuous phase modulation (CPM) is a good alternative to these modulations due to its constant envelope property which enables us to use inexpensive and energy-efficient non-linear power amplifiers. In the literature, a few works are based on relaying systems with CPM. To the best of our knowledge, none exists with relay selection. In this paper, we propose single and multiple relay selection CPM schemes based on a new generalized relay selection criterion for non-orthogonal amplify and forward (AF) systems operating with various time sharing protocols. In particular, using the proposed criterion, the best relay or the best two relays over a set of four available relays is/are selected. Error performances of the non-orthogonal AF relay selection systems and their counterparts are compared over frequency non-selective quasi-static Rayleigh fading channels using Viterbi algorithm at the destination terminal. Our numerical results present superiority of the proposed non-orthogonal relay selection systems.

Distributed space‐time trellis codes with continuous phase modulation for amplify and forward relaying

Continuous phase modulation (CPM) is a non-linear power/bandwidth efficient modulation method. Linear modulation methods such as phase shift keying or quadrature amplitude modulation produce large power drain at the power amplifier of the transmitter. Therefore CPM may be an alternative to these modulations in relay/cooperative systems because of its constant envelope property, which enables us to use inexpensive and energy-efficient non-linear power amplifiers. In this study, the authors investigate optimum distributed space-time CPM trellis codes for amplify and forward relaying systems with one to four relays and specifically consider minimum shift keying and quaternary continuous phase frequency shift keying with modulation indices of 1/2 and 1/4. Novel distributed space-time CPM trellis codes are obtained. Error performances of the novel codes and their classical counterparts are compared over frequency non-selective quasi-static Rayleigh-fading channels using the Viterbi algorithm at the destination terminal and superiority of the novel codes are presented.

L2-Orthogonal ST-Code Design for CPM

Non-linear modulations, like the Continuous phase modulation (CPM) with its constant envelope property, have been appealing for energy efficient communication systems. In parallel, linear orthogonal Space-Time block codes (STBC) have emerged as a simple way of achieving spectral efficiency by full diversity and simple decoupled maximum-likelihood decoding. However, linear codes rely on pointwise orthogonality which leads to a well-known degradation of data rate for more than two antennas. In this paper, we introduce the concept of L2-orthogonality for non-linear Space-Time codes (STC). Our approach generalizes code design based on pointwise orthogonality. Namely, we are able to derive new codes with the same advantages as pointwise orthogonal STBC, i.e. low decoding complexity and diversity gain. At the same time, we are no longer limited by the restrictions of pointwise orthogonal codes, i.e. the reduction in data rate. Actually, we show how to construct full rate codes for any arbitrary number of transmit antennas. More precisely, a family of codes for continuous phase modulation (CPM) is detailed. The L2-orthogonality of these codes is ensured by a bank of phase correction functions which maintains the phase continuity but also introduces frequency offsets. We prove that these codes achieve full diversity and have full rate. Moreover, these codes don't put any restriction on the CPM parameters.

Design Of Digital Compensation Filters In Iq Modulator By H2Norm Minimization-A State-Space Approach

Abstract In IQ modulators generating CPFSK signals, imperfections in the analogue reconstruction filters results in the loss of the constant envelope property of the output signal. Ripples in the envelope function cause spreading of the transmitted signal spectrum into adjacent channels when the signal passes through non-linear elements in the transmission path. This results in the failure to meet transmission standazd requirements. In this paper, two time-domain techniques aze proposed to compensate for the magnitude and phase characteristics of the two analog reconstruction filters. The techniques are based on the minimization of the Hz norm of the error transfer function and aze formulated using state-space equations. Simulation and implementation results are presented to illustrate the effectiveness of the new techniques.

A decorrelation constant modulus algorithm for multitarget separation using adaptive arrays

In this paper, an adaptive digital filter algorithm is presented to optimize the signal-to-noise ratio of an antenna array with multiuser signal inputs. These synchronous communication signals have constant envelope property and are transmitted through a Multiple-Input/Multiple-Output (MIMO) linear channel. This Multiuser Constant Modulus Algorithm (MU-CMA) using an antenna array can compensate for both Interuser Interference (IUI) and Intersymbol Interference (ISI). The method is derived by minimizing the cost function of the constant modulus signals as well as cross-correlations between them. The simulation result in this paper shows the performance of this algorithm.

Digital Compensation in IQ Modulator Using Optimization—A State-Space Approach

In DSP-based IQ modulators generating CPFSK signals, shortcomings in the implementation of the analog reconstruction filters result in the loss of the constant envelope property of the output CPFSK signal. These ripples cause undesirable spreading of the transmitted signal spectrum into adjacent channels when the signal passes through nonlinear elements in the transmission path and the consequent failure of the transmitted signal in meeting transmission standards requirements. Therefore, digital techniques compensating for these shortcomings play an important role in enhancing the performance of the IQ modulation system. Recently, several methods have been proposed in the literature to digitally compensate for the imperfections in the transfer characteristics of the analog reconstruction filters. Although these methods have been shown to be effective in removing the output envelope ripples, they result in filters of high orders and are therefore computationally demanding to implement on the DSP. Furthermore, previous techniques suffer from numerical instabilities as a result of matrix inversion in the process of calculating the solution vector. In this paper, we present two new techniques for designing the digital compensation filters by means of optimization to address the limitations of previous solutions. Design of control systems by optimization is now a standard technique. Simulation examples show that these techniques are effective and lead to substantial improvement of the output envelope ripples.

Indirect Cochannel Interference Cancelling

This paper describes a blind cochannel interference cancelling technique, indirect cochannel interference cancelling (ICIC), that cancels a constant envelope modulated interferer in cellular mobile radio communication channels. ICIC exploits the constant envelope property of the interfering signal to simplify the receiver structure. The basic concept of ICIC and the possible receiver structures are discussed. The performance of a ICIC receiver in practical channels as well as its sensitivities to the channel parameters are investigated by simulation.

An improvement in the performance of DS/SS/CDMA with GMSK

The CDMA system using DS/SS/GMSK modulation can realize a high spectral efficiency by using the constant-envelope property of GMSK modulation, even if the signal is band-limited and the transmitter is nonlinear. This paper discusses the optimization of a receiver in order to further improve spectral efficiency. The idea is to apply optimal weights to the despreading matrix. Using the signal-to-noise power ratio based on a linear approximation to the DS/SS/GMSK waveform, the weights that minimize the signal-to-noise power ratio are determined. The performance is compared to that of the conventional receiver, in terms of the signal-to-noise power ratio after despreading, the bit error rate, and the spectral efficiency. As a result, we show that performance is improved by applying optimal weights to the despreading matrix. © 1998 Scripta Technica. Electron Comm Jpn Pt 1, 81(6): 51–60, 1998

Constant envelope filtering of complex spreading sequences

A novel constant envelope linear root-of-unity (CE-LRU) filtering process is introduced to band limit a class of chirp-like complex spreading sequences, facilitating the application of these sequences in a fully DSP implementation of a DSSS system. The technique is unique in that it not only yields a minimum bandwidth signal, but also preserves the constant envelope property of these sequences, as well as their ideal correlation characteristics.

A comparison of fully digital quadrature modulation for modem systems

AbstractThis paper presents and evaluates the results obtained by computer simulations of different current modulation techniques by the use of DSP‐based systems and computer simulations. The modulation‐demodulation methods evaluated herein are QPSK, OQPSK, MSK, λ/4‐QPSK and Q2PSK. The constant envelope property and the relatively high power efficiency of the above‐mentioned modulation techniques makes them very suitable for digital satellite and mobile radio communications. Digital algorithms for data‐decision, carrier phase offset and timing delay estimation for each of the modems are given. Maximum likelihood carrier phase recovery performances for the different quadrature phase modulations are compared and evaluated. Results in terms of BER performances and statistical properties of the synchronization procedures are shown for the AWGN channels. Computational loads of the different modem systems evaluated are also given.

Serial MSK spread-spectrum multiple-access communications

A serial minimum-shift-keyed (MSK) direct-sequence spread-spectrum multiple-access (DS/SSMA) communication system is described and analyzed to obtain the signal-to-noise ratio. The single-channel system generates the same transmitted signals as a corresponding parallel MSK/DS/SSMA system. Hence, the transmitted signals have a constant envelope and desirable spectral properties. However, hardware is required for only one channel, and the multiple-access capability of the system compares favorably with a standard binary DS/SSMA system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

MSK-Type Reception of Continuous Phase Modulation: Cochannel and Adjacent Channel Interference

For binary continuous-phase modulation with modulation index h = 1/2 (MSK being a rather familiar example), quadrature matched-filter reception is possible with only minor degradation relative to the maximum likelihood (trellis-based) receiver. Thus this class of modulations provides good spectral attributes together with reception techniques capable of being implemented simply at high speeds. As usual, the constant-envelope property is also present. We study here the effects of interfering signals with the same modulation format, located at the same frequency (cochannel interference), or at a nearby frequency (adjacent channel interference). Coherent reception is assumed, and we analyze two channel situations: both signals nonfading with additive Gaussian noise; and both signals independently Rayleigh fading, with additive Gaussian noise. As one would expect, the smoothed phase modulation schemes have larger tolerable adjacent channel levels, while there is little differentiation in the cochannel case. We also find that MSK filters are usable for other formats with negligible loss in performance relative to the optimal linear filters, provided the filter parameters are rescaled appropriately.

The tone capture properties of CMA-based interference suppressors

An earlier paper introduced the constant modulus algorithm (CMA), an adaptive filtering technique for correcting multipath and interference-induced degradations in constant envelope waveforms such as FM and QPSK signals. This algorithm exploits the fact that both multipath propagation and additive interference disrupt the constant envelope property of the received signal. By sensing the received envelope variations, the adaptive algorithm can reset the coefficients of an FIR digital filter so as to remove the variations and, in the process, suppress the various interference components from the desired signal. This paper examines a problem that arises when using CMA to suppress narrow-band interference. If both the interferer and the signal have constant envelope and are spectrally nonoverlapping, then it is possible to find two different filter solutions, one which suppresses the interferer and another which "captures" the interferer and suppresses the desired signal. This paper examines how "capture, can occur and how it may be prevented. This problem is studied by characterizing the algorithm's behavior to an input consisting of only two sinusoids. Assuming slow adaptation, the N-dimensional adaptive weight recursion is shown to compress into a two-by-two recursion in the tone output amplitudes. This simplified recursion is then analyzed to determine what combinations of input amplitudes (signal-to-interference ratios) and filter initial conditions lead to "lock" and which lead to the capture of the interferer. The results are then broadened to include multiple input tones and signals with nonzero bandwidth.

A Class of MSK Baseband Pulse Formats with Sharp Spectral Roll-Off

Minimum frequency-shift-keying (MSK) is a very attractive modulation technique because of its spectral properties and the constant envelope property of the signal, but out-of-band energy spillover must sometimes be minimized to control co-channel interference. This problem has recently received attention in published articles and, since the pulse shape is the main parameter, many different MSK pulse formats have been described. In this note, a general shaping function, which allows various asymptotic spectral fall-off characteristics, is presented; then DSFSK (Double Sine Frequency Shift Keying) is derived from it, and its spectrum is computed, analyzed and compared with Rabzel's results.